A web address linked to the family of the disgraced Chinese politician Bo Xilai was bought from a Tenerife train enthusiast for $100,000, the Guardian can reveal.

Details of the mammoth payment for the domain guagua.com – which shares its name with Bo Xilai's son Guagua – emerged on Wednesday as the 24-year-old student broke his silence over the scandal that has enveloped his parents.

In a letter emailed to the student newspaper at Harvard, where he is studying, Bo Guagua sought to play down his wealth and reports that he led a playboy lifestyle – denying he had ever driven a Ferrari – and said his education at some of the world's leading institutions had been paid for through scholarships and family savings.

His mother, Gu Kailai, is detained on suspicion of murdering the British businessman Neil Heywood, while Bo Xilai is accused of disciplinary violations. Bo Guagua said he was "deeply concerned" but did not comment directly on the investigations into his parents.

The case has turned the spotlight on the fortunes of the wider family: the holdings of Bo and Gu's siblings have so far been calculated at $160m. Some had asked how the family could afford Bo Guagua's education on a modest official salary.

"My tuition and living expenses at Harrow School, University of Oxford and Harvard University were funded exclusively by two sources: scholarships earned independently and my mother's generosity from the savings … from her years as a successful lawyer and writer," Bo, a student at Harvard's Kennedy School of Government, wrote in a statement published by the Harvard Crimson student paper.

He added: "I have never lent my name to nor participated in any for-profit business or venture, in China or abroad. However, I have been involved in developing a not-for-profit social networking website in China … to assist NGOs in raising awareness of their social missions and connecting with volunteers. This initiative has been based out of the Harvard Innovation Lab … The project remains in the development stage and is not live."

Guagua.com is registered via a US website that protects owners' anonymity, but until last year it was registered at the same address as Guagua Technology Company, which was established with 2m yuan by Gu Wangning – Bo Guagua's aunt, who is a wealthy businesswoman.

The site has been empty – bar a form allowing visitors to register for further information – since it was bought from Antonio Marin, a 53-year-old university administrator from Tenerife, in 2010.

Marin said he initially rejected the Chinese buyer's offer for the domain name, which he used for his site on trains and trams. "I can't recall exactly who the email came from but it was not anyone called Guagua," Marin said. "Six months later they contacted me again and made me a very good offer … They did, indeed, pay me $100,000. I never asked why they wanted the site, but he made me such a good offer that I just took it."

Sedo.com, which acted as an escrow (trusted independent third party) for the deal, confirmed the price.

Reuters news agency reported that Bo's university directory page at Oxford listed him as founder of the Guagua Internet Company, while the New York Times described him as the manager and Zhang Xiaojun – the family orderly also detained on suspicion of Heywood's murder – as its supervisor. The Guardian could not confirm those details independently.

Guagua Technology at one stage boasted about 20 employees, but moved out last year, a worker in its office block said. Emails to the administrator of guagua.com and to Bo were not answered.

Bo Guagua is also listed as an adviser on the website of Oxford Emerging Markets – set up by friends from the university – which promised to "[provide] exceptional students with the opportunity to explore investment and career prospects in emerging markets", as well as organising trips to Beijing, Dubai and Hong Kong.

Co-founder George Tan said Bo Guagua was an "unofficial" adviser, but later said his name had been included by mistake.

Bo said in his statement that it was impossible to address every rumour and allegation, but defended his academic record and extra-curricular activities at Oxford, where he was rusticated (suspended) for a year.

A friend who asked to remain anonymous said that Bo Guagua was "a really good person with a good heart – very loyal and very helpful. "It is very sad what has happened to him," she said.

A Wall Street Journal article described him arriving at the residence of the then US ambassador Jon Huntsman in a red Ferrari, but Bo wrote: "I have never driven a Ferrari … nor have I ever been to the US ambassador's residence in China."

The police chief whose flight to a US consulate triggered the scandal claimed Bo's mother Gu was reported on Wednesday to have confessed to Heywood's murder with the words "I did it".

Wang Lijun – Bo Xilai's former ally and a police chief – told officials at the consulate that Heywood was held down and forced to drink cyanide after attempting to spit out the poison, the Daily Telegraph reported, citing a diplomat.